The story of that theme seems strange to me. On one hand, Raymond Chen says[1] it was a decoy in order to avoid leaking in-development Luna outside Microsoft. On the other, Microsoft’s own Office XP and VS .NET (before 2005) have styling that fits Watercolor better than it does Luna. I don’t know how to reconcile these facts.

[1] http://bytepointer.com/resources/old_new_thing/20060111_016_...